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City of Ripon Well#12 Nitrate Study Report May 31,2006 6.0 DISCUSSION OF SAMPLING RESULTS Figures 5 and 6 present the results of the nitrate sampling performed for the City of Ripon. Figure 7 presents the results of groundwater nitrate sampling performed for the RFS site. These data indicate an area of shallow groundwater nitrate concentrations significantly above the 45 mg/I MCL that is present both on the RFS site and generally to the west. The highest observed concentrations (as high as 700 mg/I) are located near the RFS liquid batch plant, and similarly high concentrations extend to the west in the general direction of shallow groundwater flow (AGE, 2005 and 2006b)4. Furthermore, low concentrations observed in some of the wells located further from the RFS liquid batch plant (MW-2, MW-3, MW-4, MW-6, MW-8, and MW-10) indicate that background nitrate concentrations are less than 45 mg/I for wells that are unrelated to the nitrate associated with the RFS site'. Figure 8 presents the nitrate concentrations collected for the city with respect to depth below ground surface and distance from the RFS liquid batch plant. As indicated, concentrations decrease with distance, both horizontally and vertically, from the liquid batch plant. 4 A wide range of information sources indicate that the prevailing direction of groundwater flow in the greater Ripon area has been westerly to northwesterly for several decades. These sources include the California Department of Water Resources (1967), The Northeastern San Joaquin County Groundwater Banking Authority(2004), The San Joaquin County Flood Control and Water Conservation District, (1988a and b, 199Da and b, 1992a and b, 1994a and b, 1996a and b),and The United States Geological Survey(1989 and 2004). 5 This observation is consistent with other data collected by the San Joaquin County Environmental Health Department provided by the attorneys for RFS. Eight of the ten water supply well samples collected in the greater Ripon area contained nitrate below the 45 mg/I MCL. Furthermore, data collected by The Source Group (2005b) also indicated background nitrate concentrations below 45 mg/I. A�wa,2R 6-1 The sourca Gawp,Inc.